1. Field of the Invention
This invention pertains generally to waveguides, and more particularly to multiple high contrast gratings configured for constraining light therebetween.
2. Description of Related Art
The ability to guide incident light and generate long optical delays with low intrinsic loss is beneficial within a wide range of applications, including optical signal processors, RF filtering, optical buffers, and optical sensing. Optical fibers have been used for these applications with advantages such as ultra-low loss, dispersion and nonlinearity, and exceedingly large bandwidth. However, optical fibers are bulky, heavy, and lack flexibility for adjustment. In response to this, lithographically defined, chip-scale waveguides have been reported in SiO2/Si and III-V material systems, which are desirable because they are compact, light-weight, and can be integrated with other optoelectronic devices. Yet, the lowest reported loss achieved to date in chip-based waveguides is on the order of 1 dB/m, which is three to four orders of magnitude higher than that exhibited by optical fibers. This loss is unacceptably high for most applications which require 0.01 dB/m, or less. The fundamental reasons for the high losses are direct band-edge absorption, free carrier absorption, and absorption due to interaction with optical phonons. In addition, these devices are expected to have high nonlinearity and dispersion.
Hollow-core waveguides (HW) are highly promising for achieving fiber-like ultra-low loss, nonlinearity and dispersion because of the elimination of the core material. There have been advances in hollow-core waveguides, ranging from waveguides using metallic shells, to ones using distributed Bragg reflectors (DBRs), to ones with photonic crystals (PhCs), and similar approaches. The basic principle is to guide the optical beam propagating through air by multiple reflections at the cladding. One hollow-core PhC optical fiber exhibits an extremely low loss of ˜0.001 dB/m; however, the lowest loss for a chip-based hollow-core waveguide is still high, at ˜10 dB/m using DBRs. The major loss in these waveguides arises from insufficient reflectivity of the cladding DBR mirrors. Ultrahigh reflectivity is essential to achieve ultra-low loss hollow waveguides.
Accordingly a need exists for a system and method of chip-scale waveguides which provide extremely low losses, but without the need of optical fibers, and more particularly hollow-core fibers. These needs and others are met within the present invention, which overcomes the deficiencies of previously developed waveguide apparatus and methods.